Answer:
B. The frequency is greater than 1.9 Hz.
Step-by-step explanation:
As we know by the equation of frequency of wave

here we know that


now from above formula we have

now it's given that when wave is travelling then temperature of the medium is heated to greater temperature.
So here energy is given by the wave to the medium so here we can say that the frequency of wave must be more than this calculated frequency as we know that this some of its energy is given to medium so that its temperature is increasing